【作者】 孙文佳；

【导师】 王青圃；

【作者基本信息】 山东大学 ， 光学工程， 2011， 博士

【摘要】 光参量振荡(Optical Parametric Oscillation, OPO)是一种实现光学频率变换的有效途径,它利用非线性晶体的混频特性,通过相位匹配获得信号光与闲频光两个波长,可实现宽频可调谐的激光输出。对于光参量振荡器的研究目前主要集中在以下几个方面：(1)以最常用的1.06μm激光作为泵浦源,通过光参量振荡产生1.5μm左右的人眼安全激光输出；(2)以1.06μm激光泵浦磷锗锌光参量振荡(ZGP-OPO),产生2μm的激光输出。由于2μm激光对大气和烟雾的穿透能力强,因而在激光雷达、激光测距、遥控传感及医学和光通讯等方面都有着重要的应用；(3)通过非线性频率变换实现中红外3-5μm的激光输出。由于3-5μm是一个重要的大气窗口波段,位于这一波段的激光对大雾、烟尘等都具有较强的穿透力,因此在雷达系统、光谱测量、激光测距、红外遥感和医学等方面都有着广泛的应用。中红外光参量振荡器一直是国内外研究的热点,它具有调谐范围宽、效率高、结构紧凑、全固化等优点,且随着各种新型优质的中红外非线性晶体的出现,使中红外光参量振荡器向世人展示出了其越来越广泛的发展前景。受激拉曼散射(Stimulated Raman Scattering, SRS)属于三阶非线性效应,也是实现激光频率变换,产生新波长的重要途径之一,频率转换后的激光波长由泵浦光波长和拉曼介质决定。通过选择不同波长的泵浦光和不同材质不同频移的拉曼介质,可以得到从紫外到近红外范围的受激拉曼散射光谱。与传统的气体和液体拉曼介质相比较,固体拉曼介质具有粒子浓度大、体积小、拉曼增益高、热传导性好、机械性能好、易于和全固态激光技术相结合等优点。以晶体作为拉曼介质的固体拉曼激光器具有结构紧凑、效率高、稳定性好等优点,在军事、医疗、交通、信息和农业等领域都有重要的应用。目前,美国、俄罗斯、澳大利亚,及中国台湾等国家和地区的研究者都在积极地参与固体拉曼激光器的研究,其中,俄罗斯的科学家在拉曼晶体生长和特性研究方面做了许多开创性的工作。我国在晶体生长领域也居世界领先水平,这为我国的固态拉曼激光器的研究提供了便利的条件。本论文主要分两部分,一部分是以Nd:YAG产生的1064 nm激光作为泵浦源,对内腔式砷酸钛氧钾(KTiOAsO4,KTA)晶体中红外波段光参量振荡器进行了理论和实验研究；另一部分是对两种新波长激光器的实验研究。本文的研究内容主要有：1.对光参量振荡中的三波互作用的基本理论进行了分析,对KTA晶体的相位匹配角和有效非线性系数进行了计算,并对非临界相位匹配理论做了介绍。2.以Nd:YAG晶体作为激光介质,KTA晶体作为非线性晶体,采用声光调Q,研究了LD端面泵浦主动调Q内腔式中红外KTA光参量振荡器的输出特性。主要包括光谱特性、功率特性、脉冲特性以及光束质量等。用1064 nm的激光泵浦11类非临界相位匹配(NCPM)的KTA晶体时,获得的信号光波长为1535 nm,获得的中红外闲频光波长为3469 nm。实验测量了不同重复频率下,中红外闲频光的平均输出功率、脉冲宽度随泵浦功率的变化关系。当LD泵浦功率为14.93 W,脉冲重复频率为40 kHz时,实验得到的中红外闲频光的最高平均输出功率为0.46 W,最高总输出功率为1.83 W,相应的由LD到参量光的光-光转换效率为12.3%。测得此时的闲频光脉宽为4 ns,获得的峰值功率为2.9 kW。此时闲频光的光束质量为12左右。3.对LD端泵、声光调Q的Nd:YAG/KTA内腔式OPO进行了理论分析,将初始反转粒子数密度和腔内光子数密度在腔内分布看作是高斯分布,而非平面波近似分布,建立了速率方程理论模型；并在求解过程中考虑了晶体的热透镜效应问题,计算了Nd:YAG晶体的热透镜焦距随泵浦功率的变化趋势,最终对速率方程进行了数值求解,并与实验结果相比较,发现理论值与实验结果较为吻合,这也证明了我们这个速率方程理论模型的正确性。4.实现了在双棒串接的LD侧面泵浦的条件下,以Nd:YAG晶体作为激光介质,以X切KTA晶体作为非线性晶体,采用声光调Q的内腔式KTA光参量振荡器的高效运转,获得的闲频光波长为3469 nm。采用串接两个相同的LD侧向泵浦Nd:YAG棒作为泵浦源,中间放入90°石英旋光片以补偿热致双折射,采用平凸腔的设计以增加稳区范围并减轻腔内高泵浦功率下热效应的影响。实验测量了不同重复频率下,中红外闲频光以及信号光的平均输出功率、脉冲宽度随泵浦功率的变化关系。当LD泵浦功率为208 W,脉冲重复频率为12.5 kHz时,实验得到的中红外闲频光的最高平均输出功率为3.4 W,此时测得的脉宽为19 ns,获得的峰值功率为14 kW。当LD泵浦功率为208 W,脉冲重复频率为7.5 kHz时,实验得到的信号光功率为12.7 W,闲频光功率为3.1 W,相应的由LD到总的参量光的光-光转换效率为7.6%,这是目前LD侧面泵浦声光调Q KTA内腔式光参量振荡的最高转换效率。5.首次实现了一种基于BaWO4晶体332cm-1频移的1103 nm的内腔拉曼激光器。以LD端而泵浦Nd:YAG晶体产生1064 nm激光作为泵浦光,选用拉曼频移为332 cm-1的46 mm长的BaWO4晶体作为拉曼介质,采用声光调Q,产生了波长为1103 nm的激光。在LD泵浦功率为7.55 W,脉冲重复率为17 kHz的条件下,获得最高的拉曼光功率为1.23 W,相应的由LD到拉曼光的转换效率为16.3%,此时拉曼光在水平和竖直方向的光束质量因子分别为2.0±0.2和1.8±0.2。同时,关于BaWO4晶体的热透镜效应问题也在给出了相应的分析。6.首次实现了氙灯泵浦的自由运转的1073.8 mm激光输出。采用平凹腔结构,用氙闪光灯泵浦尺寸为06mm×110mm的Nd:YAG晶体,产生了1073.8nm的激光输出。当输入泵浦能量为69.6 J,脉冲重复率为1 Hz时,获得的最高脉冲能量为487 mJ。本论文主要创新点如下：1.设计优化了LD端面泵浦声光调Q的中红外KTA内腔光参量振荡器,当泵浦功率为14.93 W时,获得了1.83 W的总输出功率,包括1.37 W的信号光(1.54μm)功率和0.46 W的中红外闲频光(3.47μm)功率,相应的总光-光转换效率为12.3%,这也是目前所报道的LD端泵声光调Q的中红外KTA-IOPO的最高转换效率。2.首次实现了双侧泵Nd:YAG声光调Q的KTA内腔光参量振荡器。两个完全相同的LD侧向泵浦Nd:YAG棒模块串接放置,且在两模块中放入90°石英旋光片以补偿热致双折射,这些作为泵浦源。优化了泵浦光,为下面的实验打好基础。3.实现LD双侧泵、声光调Q、Nd:YAG/KTA内腔式中红外OPO。在LD泵浦功率为208 W,脉冲重复频率为7.5 kHz时,获得的总输出功率为15.8 W,其中信号光功率为12.7 W,闲频光功率为3.1 W,相应的由LD到总的参量光的光-光转换效率为7.6%,这是目前LD侧面泵浦声光调Q KTA内腔式光参量振荡的最高转换效率。4.首次实现了一种基于BaWO4晶体332cm-1频移的1103 nm内腔拉曼激光器。采用LD端面泵浦Nd:YAG晶体,以按X(ZZ)X配置的BaWO4晶体作为拉曼介质,实现了332 cm-1频移的受激拉曼散射。在激光二极管泵浦功率为7.55W,声光Q开关工作频率为17 kHz的条件下,获得最高平均功率为1.23 W的拉曼光输出,光光转换效率达到16.3%,并估算了此时BaWO4晶体的热透镜焦距值。首次观察到了LD侧面泵浦的基于BaWO4晶体332cm-1频移的1103nm的拉曼激光输出。5.首次实现了氙灯泵浦Nd:YAG自由运转的1073.8 nm激光输出。当输入泵浦能量为69.6J,脉冲重复率为1 Hz时,获得的最高脉冲能量为487 mJ,并测量了脉冲特性和光束质量特性。更多还原

【Abstract】 Optical Parametric Oscillation (OPO) is an attractive method of frequency conversion. It uses the mixing characteristics of the nonlinear crystal and phase matching method to obtain broadband tunable output laser. OPOs usually focus on the following aspects:(1) The matured 1.06μm laser is used as the pump source to realize the eye-safe wavelength region. (2) The matured 1.06μm laser is used as the pump source to pump ZnGeP2 crystal and realize the 2μm region laser. Because this region has high ability to go through the atmosphere and smoke, so it has many important applications in laser radar, laser ranging, remote sensing and optical communications, etc. (3) By nonlinear frequency conversion technology, the mid-infrared 3-5μm region laser is realized. Because 3-5μm is an important atmospheric window, the laser under this region has very strong transmittance, which makes it feasible for wide applications in such field as radar system, spectral measurement, laser ranging, infrared remote sensing and other aspects. Mid-infrared OPO has been the hot research at home and abroad. It takes advantages of wide tunable region, high efficiency, compactness and high stability. And with the development of new high-quality mid-infrared nonlinear crystals, the mid-infrared OPO shows the much wider applications.Stimulated Raman scattering (SRS) is an attractive method of frequency conversion based on the third-order nonlinear optical effect. The wavelength of the scattered light is determined by the wavelength of the pumped light and the Raman shift of the Raman-active media. By selecting different pumping sources and Raman-active media, the laser spectrum reachable with SRS can extend from the ultraviolet to the near infrared. Compared with the conventional gases and liquids media, the solid-state Raman-active media offer high molecule density, high gain, favorable thermal and mechanical properties, and compatibility with the compact all solid-state laser technology. Hence they can find important applications in many fields such as national defence, medicine, traffic, information, industry and agriculture. So far, the researchers from USA, Russia, Australia and Taiwan are taking part actively in the field of the all-solid-state Raman lasers. Especially the scientists of Russia act as the leading role in the regime of Raman crystal growth and research on the solid state Raman lasers. China is renowned for the advanced crystal growth technology, and this provides favorable conditions to the study of all-solid-state Raman lasers in China.There are two parts in this dissertation. One is the theoretical and experimental studies on KTA intracavity optical parametric oscillator pumped by Nd:YAG laser. The other is the research on two kinds of new wavelength lasers. The main content of this dissertation is as follows:1. We analysis the three-wave interaction theory in optical parametric oscillation. We calculate the angle of phase-matching and the effective nonlinear coefficient of KTA crystal, and introduce the noncritical phase matching.2. By using Nd:YAG crystal as the laser gain medium (1064.2 nm), KTA as the nonlinear crystal, the diode-end-pumped acousto-optically (AO) Q-switched intracavity OPO (IOPO) is studied. The various characteristics are studied, e.g. spectrum, output power, conversion efficiency and beam quality. The signal wavelength and the idler wavelength in this case are determined to be 1535 nm and 3469 nm. The output powers and pulse widths are measured with different pump powers and different pulse repetition rates (PRRs). When the diode power is 14.93 W and the PRR is 40 kHz, an output mid-infrared idler power of 0.46 W is obtained, the total output power of 1.83 W, corresponding to an optical-to-optical (diode power to total power) conversion efficiency of 12.3%. Under the same condition, the pulse duration of idler wave is 4 ns, corresponding to the peak power of 2.9 kW. The beam quality factors (M2) of idler wave is about 12.3. Theoretical analyses are performed to study the output characteristics of the diode-end-pumped AO Q-switched Nd:YAG/KTA IOPO. By regarding the initial population inversion density (IPID) and the intracavity photon densities as Gaussian distributions, the rate-equation model is deduced. Thermal lens effect in the Nd:YAG crystal is also considered. The thermal focal lens of Nd:YAG crystal is calculated with different pump powers. The theoretical results are in good agreement with the experimental data, which confirms the applicability of the theoretical model.4. A high efficiency KTiOAsO4 (KTA) intracavity optical parametric oscillator (IOPO) pumped by a diode-side-pumped acousto-optically (AO) Q-switched two-rod Nd:YAG laser is demonstrated. The pump source is a diode-side-pumped two-rod Nd:YAG laser. A 90°quartz rotator is inserted between the two Nd:YAG modules to compensate the birefringence. The output powers including signal power and idler power, and pulse widths are measured with different pump powers and different pulse repetition rates (PRRs). When the diode power is 208 W and the PRR is 12.5 kHz, the highest output mid-infrared idler power of 3.4 W is obtained. When the diode power is 208 W and the PRR is 7.5 kHz, the highest output total power of 15.8 W is obtained, corresponding to an optical-to-optical conversion efficiency of 7.6%, which is the highest conversion efficiency in diode-side-pumped KTA IOPOs to our knowledge.5. A compact efficient Raman laser at 1103.2 nm is realized within a diode-end-pumped acousto-optically Q-switched 1064.2 nm Nd:YAG laser. A 46-mm-long BaWO4 crystal is used as the active medium and its 332 cm-1 Raman mode is employed to finish the conversion from 1064.2 nm fundamental laser to 1103.2 nm Raman laser. At an incident pump power of 7.55 W, the first-Stokes power of 1.23 W at 1103.2 nm is obtained at a repetition rate of 17 kHz, corresponding to a diode-to-Stokes conversion efficiency of 16.3%. The Raman beam quality factors (M2) in the two orthogonal directions are 2.0±0.2 and 1.8±0.2, respectively. The thermal focal length of the BaWO4 crystal is estimated.6. A flash-lamp pumped Nd:YAG laser emitting 1073.8 nm is demonstrated. A concave-plane cavity is employed, and Nd:YAG rod with a size of (?)6 mm×110 mm. With incident pump energy of 69.6 J and pulse repetition rate of 1 Hz, output pulse energy of up to 487 mJ is obtained. The main innovations of this dissertation are as follows:1. Diode-end-pumped AO Q-switched intracavity Nd:YAG/KTA mid-infrared OPO is optimal designed. When the diode power is 14.93 W and the PRR is 40 kHz, an output mid-infrared idler power of 0.46 W is obtained, the total output power of 1.83 W, corresponding to an optical-to-optical conversion efficiency of 12.3%. This is the highest efficiency reported for the diode-end-pumped AO Q-switched intracavity mid-infrared KTA OPOs.2. Diode-side-pumped acousto-optically (AO) Q-switched two-rod Nd:YAG mid-infrared KTA-IOPO is reported for the first time. The pump source is a diode-side-pumped two-rod Nd:YAG laser and a 90°quartz rotator is inserted between the two Nd:YAG modules to compensate the birefringence. All this design optimize the pump source.3. A high efficiency KTiOAsO4 (KTA) intracavity optical parametric oscillator (IOPO) pumped by a diode-side-pumped acousto-optically (AO) Q-switched two-rod Nd:YAG laser is demonstrated. The highest average output power of 12.7 W at 1.54μm and 3.1 W at 3.47μm are obtained at the pulse repetition rate (PRR) of 7.5 kHz under the diode power of 208 W, corresponding to an optical-to-optical conversion efficiency of up to 7.6%. This is the highest conversion efficiency in diode-side-pumped KTA IOPOs to our knowledge.4. Diode -end-pumped compact efficient Nd:YAG/BaWO4 Raman laser at 1103.2 nm based on the Raman shift of 332 cm-1 is reported for the first time. At an incident pump power of 7.55 W, the first-Stokes power of 1.23 W at 1103.2 nm is obtained at a repetition rate of 17 kHz, corresponding to a diode-to-Stokes conversion efficiency of 16.3%. The thermal focal length of the BaWO4 crystal is estimated. Diode -side-pumped Nd:YAG/BaWO4 Raman laser at 1103.2 nm is reported for the first time.5. A flash-lamp pumped Nd:YAG laser emitting 1073.8 nm is demonstrated for the first time. With incident pump energy of 69.6 J and pulse repetition rate of 1 Hz, output pulse energy of up to 487 mJ is obtained.更多还原